1. Field of the Invention
This invention relates to an anchoring device for anchoring a grid relative a frame member of a filter pan. More particularly, this invention relates to an anchoring device for anchoring a grid relative the sidewall or a grid bar of a filter pan used in the production of phosphates.
2. Information Disclosure Statement
Because of the ever increasing demand for phosphates as agricultural soil fertilizers, the manufacture of phosphates from phosphoric ore has become a major industry. Various processes have been employed in obtaining phosphates from the phosphoric ores but these processes generally fall into two categories. First, the elemental phosphorus process and second, the wet acid process. The wet acid process involves crushing and grading raw phosphate rock known as Fluorapatite and treating this crushed rock with an acid such as sulfuric acid to obtain a single, super-phosphate which is a mixture of calcium sulfate and monocalcium phosphate.
In the wet acid process, the crushed Fluorapatite is treated with sulfuric acid in a digester. Slurry from the digester is then fed to a filtration unit where phosphoric acid is separated from the calcium sulfate precipitate. This separation is carried out by the application of partial vacuum applied to the underside of the filter element.
A typical filtration unit utilized in the phosphate industry for the separation of calcium sulfate is of generally circular configuration. The filtration unit includes twenty-four filter pan cells of substantially trapezoidal shape arranged as partial sectors of the circular filtration unit. Each filter pan cell is provided with means to enable the pan to rotate about a radial axis of the circular unit.
The filter pans are driven about a vertical axis of the circular unit so that each filter pan will progressively pass through various stations. At the first station, the pan is filled with feed slurry from the digester. When the pan has been filled, partial vacuum is applied to the underside of the filter element to draw off an undiluted mother liquor, which is phosphoric acid. At the next station, the filter pan, which now contains a filter cake of calcium sulfate, is sprayed with a weak wash liquor returned from the operation performed on the filter cake at the next station. Vacuum is again applied to the underside of the filter element to draw off the strong wash liquor having a concentration of phosphoric acid less than the undiluted mother liquor extracted at the first station. During the next station, wash water is applied to the calcium sulfate filter cake while vacuum is applied to extract a weak wash liquor which is returned to the second station for spraying onto the filter cake. The next station includes rotation of the filter pan cell to invert the pan to empty the filter cake therefrom. At this station, instead of a vacuum, air is blown through the underside of the filter element to dislodge the filter cake. At the following station, water is sprayed upwardly into the inverted filter pan to clean the pan of calcium sulfate precipitate. The pan is then dried and ready to receive the next supply of slurry from the digester.
The above filtration unit thus operates on a continuous basis with filter pans rotating through all of the above stations every 3 to 5 minutes. After prolonged usage of the filter pan, there is a tendency for a build-up of corrosive calcium sulfate precipitate that becomes lodged between the filter grid and the filter pan sidewalls. The same build-up of precipitate occurs between the grid and the grid bars. Because of this build-up, the efficiency with which the filter pan can operate is impaired and the rate at which air can pass through the grid is decreased. Therefore, it becomes necessary for the grid to be periodically removed from the filter pan to permit the calcium sulfate to be chiseled out of the filter pan and removed from the same. It will be evident to those skilled in the art that such removal of the grid from the filter pan presents serious problems.
First, the whole filter unit must be shut down to permit removal of the grid from the filter pan. This shutdown of the filter unit obviously interrupts production of phosphates. Second, because of the corrosive nature of the calcium sulfate precipitate, removal of the bolts from the filter pan to allow disengagement of the grid from the pan often results in bolts snapping within the filter pan.
Usually the base of the filter pan is provided with a plurality of internally threaded bosses. The bosses are welded to the base of the filter pan and the grid is laid over the top of the bosses. The edges of the grid fit within the area defined by the sidewalls of the filter pan. Apertures defined by the grid register with the internally threaded bosses such that bolts can be inserted through the apertures to threadably engage the bosses. When a threaded bolt snaps within the boss, it becomes necessary to ream out the bore of the boss to remove the broken end of the bolt. The oversize bore must then be internally threaded and an oversize bolt must be provided to cooperate with the replacement threaded bore. All of these operations are extremely time-consuming and not only result in high cost of maintenance, but also results in a considerable loss in production.
The present invention overcomes the aforementioned inadequacies of the known anchoring devices by providing a tapered or tapered pin which cooperates with a strap secured to the filter pan. The tapered pin effectively wedges between the strap and the base of a housing secured to the grid.
The anchoring device of the present invention provides a quickly released mechanism for anchoring the grid onto a filter pan. The anchoring device requires no special tools for installation and reliably secures the grid to the filter pan even when subjected to prolonged vibration. Therefore, it is the primary object of this invention to provide an anchoring device for anchoring a grid relative a frame member of a filter pan which overcomes the aforementioned inadequacies of the prior art devices and provides an improvement which significantly contributes to the ease with which a grid can be removed from a filter pan for cleaning purposes.
A further object of the present invention is the provision of a tapered pin which cooperates with an inverted U-shaped strap which is rigidly secured to either the sidewall of the filter pan or a grid bar of the same.
A further object of the present invention is the provision of an open topped housing which is rigidly secured to the grid with the open top of the housing registering with an aperture defined by the grid.
A further object of the present invention is the provision of an orifice defined by the base of the housing, the orifice removably receiving therein the inverted strap such that when the strap is inserted through the orifice, the tapered pin is inserted through the strap to wedge the pin between the strap and the base of the housing.
A further object of the present invention is the provision of a box-shaped housing having an open top which is of the same dimensions as the aperture of the grid.
A further object of the present invention is the provision of a cantilevered bracket having a first and a second end, the first end being rigidly secured to a grid bar and the second end being rigidly secured to the free ends of the U-shaped strap.
A further object of the present invention is the provision of a cantilevered bracket having a first and a second end, the first end being rigidly secured to a framework which is rigidly secured to a sidewall of the filter pan. The second end of the cantilevered bracket is rigidly secured to the free ends of the U-shaped strap.
A further object of the present invention is the provision of a tapered pin having a bottom surface which cooperates with the base of the housing and a top surface including a tapered surface which cooperates with the U-shaped strap.
Another object of the present invention is the provision of a forward end of the bottom surface of the tapered pin, the forward end being curved for permitting the engagement of the forward end of the tapered pin between the U-shaped strap and the base of the housing.
Another object of the present invention is the provision of a locking link pivotably secured to the rearward end of the tapered pin, the locking link defining at the distal end thereof a hole which aligns with a complimentary hole defined by an extension of the grid. The holes of the locking link and the extension of the grid are aligned when the tapered pin is wedged between the U-shaped strap and the base of the housing and a locking pin is inserted through the aligned holes to lock the link and the tapered pin in the wedged position.
The foregoing has outlined some of the more pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description describing the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.
This invention should not be construed as limited to an anchoring device for anchoring a grid to the frame member of a filter pan for the production of phosphates, but should include other applications in which a grid should be easily removable from the framework of a filter pan or the like.